The present invention relates to a method of preparing a guanosine-group compound, which is used as a raw material of an anti-virus agent, antisense medicine and the like, and a method of preparing a glyoxal-guanosine-group compound as an intermediate of the guanosine-group compound.
Guanosine or 2′-deoxyguanosine is industrially produced mainly by extraction/separation of hydrolysate of DNA (deoxyribonucleic acid) or RNA (ribonucleic acid), because the yield is extremely low when guanosine or 2′-deoxyguanosine is chemically synthesized. However, the hydrolysate of DNA contains 2′-deoxyadenosine, 2′-deoxycytidine and thymidine other than the targeted 2′-deoxyguanosine. The hydrolysate of RNA contains adenosine, cytidine and uridine other than the targeted guanosine. Accordingly, in order to collect only guanosine or 2′-deoxyguanosine, it is necessary to perform complicated processes of extraction/separation, thereby inevitably raising the production cost.
On the other hand, a method has been reported in which nucleoside (or deoxynucleoside) and nucleic acid base, which are the raw materials, are subjected to a base-exchange reaction by nucleoside phosphorylase, whereby the aimed nucleoside (or the aimed deoxynucleoside) is obtained (Hori, N., Watanabe, M., Yamazaki, Y., Mikami, Y., Agric. Biol. Chem., 53, 197–202 (1989)). By this method, adenosine and 2′-deoxyadenosine can be easily prepared (Jpn. Pat. Appln. KOKAI Publication No. 11-46790 “Method of preparing a purine nucleoside compound”). In order to obtain guanosine and 2′-deoxyguanosine by this method of enzymatic synthesis reaction, guanine must be soluble to water at least in a range of pH where the enzymes necessary for the reaction can function. In general, it is considered that the solubility of the reaction substrate is preferably at least equal to the concentration of Michaelis constant (Km) of the enzyme or higher, in order to carry out the enzyme reaction smoothly. However, as the solubility of guanine to water does not exceed a few ppm the above method of enzymatic synthesis reaction cannot be employed in practice. Due to such an impasse-like situation, it has been demanded to develop a method of efficiently preparing guanosine or 2′-deoxyguanosine.